docs: def getfullnameof(mod, xtrapath=None):
      """
      Return the full path name of MOD.
  
      MOD is the basename of a dll or pyd.
      XTRAPATH is a path or list of paths to search first.
      Return the full path name of MOD.
      Will search the full Windows search path, as well as sys.path
      """
      # Search sys.path first!
      epath = sys.path + winutils.get_system_path()
      if xtrapath is not None:
          if type(xtrapath) == type(''):
              epath.insert(0, xtrapath)
          else:
              epath = xtrapath + epath
      for p in epath:
          npth = os.path.join(p, mod)
          if os.path.exists(npth):
              return npth
          # second try: lower case filename
          for p in epath:
              npth = os.path.join(p, mod.lower())
              if os.path.exists(npth):
                  return npth
      return ''